There were certainly very public signs before that. Hitler had _tried_ to seize power:
> The Beer Hall Putsch was a failed coup d'état by the Nazi Party leader Adolf Hitler to seize power in Munich, Bavaria, which took place in November in 1923. 603 SA [Sturmabteilung - Storm Detachment, the Nazi's original paramilitary unit] surrounded the beer hall. Hitler, surrounded by his associates, advanced through the crowded auditorium. Hitler fired a shot into the ceiling and jumped on a chair yelling: "The national revolution has broken out! The hall is filled with six hundred men. Nobody is allowed to leave." He went on to state that the Bavarian government was deposed and declared the formation of a new government.
> Following the initial failure of the putsch, approximately two thousand Nazis were marching to the Feldherrnhalle, when they were confronted by a police cordon, which resulted in the deaths of 16 Nazis and four police officers. Hitler, who was wounded during the clash, escaped immediate arrest; after two days, he was arrested and charged with treason.
> The putsch brought Hitler to the attention of the German nation and generated front-page headlines in newspapers around the world. Hitler was found guilty of treason and sentenced to five years in Landsberg Prison.[1]
Mein Kampf has had also been published by 1926, sections of which gave a rather stark insight into Hitler's thought process:
> At the beginning of the War, or even during the War, if twelve or fifteen thousand of these Jews who were corrupting the nation had been forced to submit to poison-gas, just as hundreds of thousands of our best German workers from every social stratum and from every trade and calling had to face it in the field, then the millions of sacrifices made at the front would not have been in vain. On the contrary: If twelve thousand of these malefactors had been eliminated in proper time probably the lives of a million decent men, who would be of value to Germany in the future, might have been saved.[2]
[1] Paraphrased from https://en.wikipedia.org/wiki/Beer_Hall_Putsch
[2] James Murphy translation - http://gutenberg.net.au/ebooks02/0200601.txt ; the original German can be found at "Hätte man zu Kriegsbeginn..." in this document: https://ia802801.us.archive.org/9/items/Hitler-Adolf-Mein-Ka...